1 Field of Invention
This invention relates to a camera, and in particular, to a camera (inclusive of a movie video camera and a still video camera) which is required to adjust a white balance of video signals representing an image of a subject and a camera which senses light from the outside thereof and provides various controls based on the sensed light.
2 Description of the Related Art
Since a video camera is adapted to process color video signals, it is required to adjust a white balance of chrominance signals. Conventional video cameras are equipped with a color temperature sensor for measuring the color temperature of illuminating light inclusive of sunlight such that a white balance adjustment is carried out depending on the color temperature sensed by the sensor.
The color temperature sensor senses red and blue components of light incident thereto and measures the color temperature of incident light by computing the ratio of quantity of light between these two components. In a case where the incident light is natural light, since the color temperature can be sensed so as to obtain a relatively correct result, a satisfactory reproduction of the color of the subject may thereby be achieved. However, when sensing red and blue components of incident light, the color temperatures of sunlight (outdoors in fine weather) and fluorescent light (particularly daylight-cool white fluorescent lamp) sensed by the color temperature sensor show substantially the same value. Consequently, it is difficult to correctly distinguish between the sunlight and fluorescent light. As a result, in the case where the photograph is taken under fluorescent light, there arises a problem for a satisfactory reproduction of the color of a subject to.
On the other hand, in a camera having an automatic exposure control function, a quantity of incident light (luminance of a subject) is measured by a photometry element, and an exposure value is determined based on the measured quantity of incident light. As described above, in the camera adapted to process color video signals, it is required to adjust the white balance of chrominance signals. In order to adjust the white balance, the color temperature is sensed by the color temperature sensor.
In a camera system in which signals detected by the photometry element or color temperature sensor are sampled over a number of times at a fixed period or at a predetermined interval so as to be supplied to a control device (e.g., a CPU such as a microprocessor), the following problems arise in relation to artificial light. That is, the incandescent electric light and fluorescent light include ripple components of which the frequency is two or four times as high as that of the commercial frequency, so that depending on the sampling period and sampling time zone, only bright parts or dark parts are sampled and hence an average quantity of incident light cannot be obtained.